Method and system for Doppler frequency estimation

Abstract

A method is provided for determining the Doppler frequency shift that occurs in the reception of a communication signal when the relative velocity between the transmitted and receiver is unknown. By estimating the channel characteristics and measuring the channel response to known transmitted data bits, a measure of the Doppler frequency is determined according to the method of the invention. In particular, a good estimate of the Doppler frequency shift is obtained based on a second order statistic of the fading process for the channel response to the known transmitted data bits. The approach is simple and general. It applies for any system such as WCDMA and CDMA 2000 when Doppler frequency is needed.

What is claimed is:  
     
       1. In a wireless communication system wherein a fading process for a channel in said communications system is characterized by a known channel fading process, a method for determining a Doppler frequency shift induced in a signal between two stations comprising the steps of: 
       determining a value for an auto-correlation function of said channel fading process based on a signal received from said channel, said auto-correlation function having a Doppler frequency component; and  
       estimating said Doppler frequency shift as a function of said determined auto-correlation function value;  
       wherein said function of said determined auto-correlation function value for estimating said Doppler frequency shift is specified as          f   m     =       1   π                  R   uu          (     t   2     )       -       R   uu          (     t   1     )             (       t   1     +     t   2       )          (       t   1     -     t   2       )                             
       where f m  is the estimated Doppler frequency, R uu (τ) is an auto-correlation function value for the received signal and t 1  and t 2  are any two symbol locations for the received signal.  
     
     
       2. The method as recited in  claim 1  wherein said received signal auto-correlation function value is determined in relation to a received signal at a first symbol location and a received signal at a second symbol location. 
     
     
       3. The method as recited in  claim 2  wherein said received signal at said first symbol location and said received signal at said second symbol location are determined in reference to transmitted signals having known values. 
     
     
       4. The method as recited in  claim 1  wherein said channel fading response model is based on a Rayleigh channel. 
     
     
       5. The method as recited in  claim 1  wherein said channel fading response model is based on a Rician channel. 
     
     
       6. A method for determining a Doppler frequency shift induced in a channel between two stations of a wireless communications system, the channel being characterized in terms of a known channel fading process, the method comprising the steps of: 
       receiving a signal from said channel;  
       extracting from said received signal a symbol value received at first and a second symbol locations;  
       determining an auto-correlation for said extracted received symbol values based on an auto-correlation function for said known channel fading process; and  
       computing an estimated Doppler frequency shift for said channel as a function of said determined auto-correlation according to the relation:          f   m     =       1   π                  R   uu          (     t   2     )       -       R   uu          (     t   1     )             (       t   1     +     t   2       )          (       t   1     -     t   2       )                             
       where f m , is the estimated Doppler frequency, R uu (τ) is the determined auto-correlation for the received symbol values and t 1  and t 2  are temporal values for said first and second symbol locations.  
     
     
       7. The method of  claim 6  wherein said received symbol values are pilot signal values.